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Date and Time of the Query: 2019-06-20 T14:46:34 PDT
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For refcode 1989ApJ...345..730P:
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Copyright by American Astronomical Society. Reproduced by permission
1989ApJ...345..730P THE CIRCUMNUCLEAR ENVIRONMENT OF NEARBY, NONINTERACTING SEYFERT GALAXIES RICHARD W. POGGE Lick Observatory, Board of Studies in Astronomy and Astrophysics, University of California, Santa Cruz Received 1988 December 16; accepted 1989 April 13 ABSTRACT An investigation into the physical conditions prevailing in the regions immediately surrounding the active nuclei in 20 nearby, noninteracting Seyfert galaxies is reported. CCD interference-band images isolating the bright emission lines of H{alpha} + [N II] and [O III] {lambda}5007 have been obtained to search for spatially extended circumnuclear emission regions. Long-slit, low-resolution spectrophotometry of interesting cases was used to probe the ionization state of the extended emission regions. Only three out of nine Seyfert 1 galaxies have spatially extended ionized gas regions, compared with eight out of 11 Seyfert 2 galaxies. Enhanced circumnuclear star formation is uncommon to both Seyfert 1 and 2 galaxies. Extended emission in Seyfert 1 galaxies has nearly the same morphology in both H{alpha} + [N II] and [O III] emission. In the Seyfert 2 galaxies, the H{alpha} + [N II] and [O III] images show different extended emission morphologies. The [O III] emission regions appear as either one- or two-sided structures, four of which are resolved into distinct cones of high-ionization gas emanating from the active nucleus. Spectra of these extended regions show the gas to be in a high excitation state, consistent with photoionization by a hard-photon spectrum, possibly the nuclear continuum. For Seyfert 1 and 2 galaxies with published radio maps, the radio continuum and optical emission-line structures appear roughly aligned, but are not correlated knot-for-knot. The morphology and ionization of these regions suggests anisotropy of the nuclear ionizing continuum. Ionizing radiation cones like those observed are predicted by models of Seyfert nuclei in which Seyfert 2 galaxies are Seyfert 1 nuclei "hidden" from our line of sight. However, this model may only apply to some Seyfert 2 galaxies, since there are significant differences between Seyfert 1 and 2 galaxies in their circumnuclear properties which are not easily reconciled with this simple "unified" picture. Subject headings: galaxies: nuclei - galaxies: Seyfert - galaxies: structure
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